The present invention relates to a shift-assisting device which enables the shifting operation to be executed with a decreased force in changing the speed of a transmission mounted on a vehicle.
Large trucks and buses that require a large shifting force for changing the speed have been equipped with a shift-assisting device for executing the shifting operation with a decreased force. The shift-assisting device with which large vehicles are furnished, generally, uses a compressed air as a source of operation. The shift-assisting device that uses the compressed air as the source of operation is equipped with a shift actuator comprising a pneumatic pressure cylinder that operates the speed-change operation mechanism coupled to a speed-change lever in the direction same as the direction in which the speed-change lever is shifted. Large vehicles generally use the compressed air as a source for operating the brake and are, hence, allowed to use the compressed air for the shift-assisting device. However, small- and medium-sized vehicles that are not equipped with a compressor as a source of the compressed air, cannot be provided with the shift-assisting device that uses a shift actuator which comprises a pneumatic pressure cylinder. In recent years, however, it has been demanded to provide even small- and medium-sized vehicles with the shift-assisting device, and there have been proposed shift-assisting devices using an electric motor as taught in, for example, Japanese Laid-open Patent Publication (Kokai) No. 87237/1993 (JP-A 5-87237) and Japanese Patent No. 2987121. In the shift-assisting device using the electric motor, it is desired that the driving force of the electric motor is controlled depending upon the manner of operating the speed-change lever by a driver so that a smooth shifting operation can be conducted. According to the shift-assisting devices disclosed in the above Japanese Laid-open Patent Publication (Kokai) No. 87237/1993 and Japanese Patent No. 2987121, a force for an operation of the speed-change lever toward the direction of shift is detected and the driving force of the electric motor is controlled according to this force of operation. Further, Japanese Patent No. 2987121 discloses a technology in which the speed of a shifting operation is detected and an increasing rate of the driving force of the electric motor is increased with an increase in the speed of the shifting operation.
In shifting the transmission equipped with a synchronizing mechanism, the largest operation force is required for bringing the gears into engagement in a synchronizing operation in the gear-engaging operation, and then, a second largest force is required for engaging the chamfer of dog teeth with the chamfer of spline of the clutch sleeve. And, in an gear-disengaging operation, an operation force is required during from the start of the gear-disengaging operation until when the dog teeth are disengaged from the spline of the clutch sleeve. In the shift-assisting device for controlling the driving force of the electric motor according to the operation force, however, the electric motor is driven after the operation force has reached a predetermined value and hence, there exists a time lag until the assisting force is produced after the operation force has increased. In shifting the transmission, therefore, the driver feels a large force just before the assisting force is produced by the electric motor. In order to solve this problem, the present applicant has proposed in Japanese Patent Application No. 46173/2000 a shift-assisting device for a transmission, equipped with a shift stroke sensor that detects the shift stroke position of the shifting mechanism and controls the electric motor for assisting the shifting operation correspondingly to the shift stroke position based on a detection signal from the shift stroke sensor.
In the shift-assisting device for a transmission in which the shift-assisting electric motor is controlled in response to the shift stroke position, the shift-assisting force corresponding to the shift stroke position can be obtained thereby to prevent the occurrence of time lag from the shifting operation. Even when an operation force is small, however, a predetermined assisting force is produced at a predetermined shift stroke position and consequently, it often happens that the assisting force does not match with the driver""s operation feeling.
It is an object of the present invention to provide a shift-assisting device for a transmission, which is capable of producing an assisting force close to the driver""s operation feeling that meets the shift stroke position and the shifting force.
In order to accomplish the above-mentioned object, the present invention provides a shift-assisting device for a transmission, equipped with an electric motor for operating a shifting mechanism in a direction same as the direction of shifting operation of a speed-change lever, the shifting mechanism being coupled to the speed-change lever to actuate the synchronizing mechanism of the transmission, wherein the shift-assisting device for a transmission comprises:
a shift stroke sensor for detecting a shift stroke position of the shifting mechanism;
a shifting force sensor for detecting a shifting force of the speed-change lever; and
a controller for controlling the electric power for driving the electric motor based on the signals from the shift stroke sensor and said shifting force sensor;
the controller determining the driving electric power depending on the shift stroke position detected by the shift stroke sensor and on the shifting force detected by the shifting force sensor.
The electric power for driving the electric motor is obtained by multiplying a multiplying factor set correspondingly to the shift stroke position, a shifting force and a predetermined constant.